From the guys who made some well known 3 blades :
Black the cutting edges, put the head on a shaft, grind 2 blades at a time on a fine 6" grinding wheel,
[ LIGHTLY] , keep turning and equal number of strokes on each pair of blades til the black is gone.
I like to go from back of blade to point to keep the point even, just pull the arrow in a straight line.
Then a fine file to the now hollow ground edge, again 2 blades at a time. Light strokes, all you need to do is clean up the edge slightly.
I can sharpen my VPA 200s or Woodsman blades in about 3 minutes start to finish.
May not be for everyone but I won't sharpen any other way now....